The Breen (Second Human Empire: ?) were a reclusive, powerful, and warlike humanoid race, native to the planet Breen in the Alpha Quadrant. They are collectively secretive; as of the 2200 N.E, not even their allies knew much about their species or their homeworlds. Some time before the Nationalist Wars, they became affiliated with the Hegemony of Independent States. They are similar to the Ubeses in the Filo and Viau universe. They joined the Coalition of Independent States. Thot Gor is one well-known individual of the Breen
Very little is known about the Breen. They are thought to be humanoid, as they appear to be of typical humanoid height and build, though Anya Oliwa speculated that they had a wolf-like appearance, and xenologists speculated that the Breen could be a silicon-based lifeform. No one has seen the Breen outside of their sealed, refrigerated suits of armor; it is said that those who have did not live to tell of it. Since it had been reported that the Breen homeworld was a frozen wasteland, it was thought that the refrigerated suits were intended to keep them comfortable in warmer alien climates, though Weyoun once mentioned that Breen is "actually quite comfortable", leaving the purpose of their suits a source of speculation.
It was speculated that the Breen body may be composed of ammonia and gelatin, which are held together in freezing temperatures but evaporate in warmer temperatures. Evaporation upon contact with warm temperature would account for why Anya Oliwa and Solas failed to report on the Breen appearance after stealing the suits of two Breen guards. They likely have a skeletal structure but, as they have no blood, contain few organs. The internal structure of the Breen body is said to consist of layers of gelatin-filled chambers, with the gelatin serving a similar function to blood, as it transfers chemicals vital for bodily functions. Therefore, when a Breen sustains an injury, a layer of gelatin will clot around it and seal the wound, which will leave a scar if left untreated